Children's ride-on vehicles are reduced-scale vehicles that are designed and sized for use by children. For example, children's ride-on vehicles include a seat adapted to accommodate one or more children as well as steering and drive assemblies that are adapted to be operated by a child sitting on the seat. The drive assembly is adapted to drive the rotation of one or more of the vehicle's wheels and may include a battery-powered motor assembly or a manually powered drive assembly, such as a pedal-powered drive assembly.
The wheels used on children's ride-on vehicles are often blow-molded from a suitable material, such as a plastic. Blow-molded wheels are conventionally formed using a mold that has two portions, which typically separate in an axial direction. The portions of the mold collectively define a cavity that defines, or corresponds to, the shape of the blow-molded wheels, including the tread surface. The seam, or part line, between the axially-separating mold portions typically defines, or corresponds to, the central circumferential portion of the wheel. During the blow-molding process, a parison of molten plastic is introduced into the mold cavity and a pressurized gas, such as air, is used to force the molten plastic against the internal surface of the cavity in order to form a hollow wheel having a shape defined by the internal surface of the cavity. After a cooling period, the mold portions are separated, and the blow-molded wheel is removed.
Blow-molded articles, including blow-molded wheels, as well as the corresponding molds and processes used to produce such articles, should be configured to permit removal of the finished article from the mold without deforming, tearing, or otherwise damaging the finished article. Projections or hollows on the surface of a blow-molded article typically correspond to hollows or projections on the inner surface of the corresponding mold. Removal of a completed blow-molded article from its mold withdraws the mold projections from hollows on the blow-molded article. Similarly, the projections on the surface of the blow-molded article are removed from the hollows on the inner surface of the mold during mold removal. When such projections or hollows are oriented generally parallel to the direction of mold removal, the projections on the mold or article are simply pulled out of the corresponding hollow during mold removal. In contrast, when the projections or hollows on a blow-molded article are not oriented generally parallel to the direction of mold removal, such as when they are oriented generally perpendicular to the direction of mold removal, such projections or hollows may be said to overlap corresponding portions of the mold with respect to the direction of mold-removal. Blow-molded articles that have projections or hollows that overlap corresponding portions of the mold with respect to the direction of mold-removal are commonly referred to as being “undercut.”
Small undercuts may be permissible because blow-molded articles tend to shrink slightly during cooling, such that the article may pull away from the mold and release the overlap. Further, blow-molded articles may permit a small amount of elastic deformation or deflection, which may be sufficient to release small undercuts. However, undercuts over a certain threshold may effectively lock a blow-molded article into its mold. In particular, if an undercut is too large, the shrinkage and/or potential elastic deformation of the blow-molded article may be insufficient to permit removal of the finished article without damage. Conventionally, blow-molded wheels must have undercuts of ⅛ inch (3.175 millimeters) or less so that they may be removed from the molds used to form the wheels.
As discussed above, blow-molded wheels are typically blown in a mold that opens in an axial direction. By using a mold that opens in an axial direction, blow-molded wheels may have significant axially oriented projections or hollows, such as may be used to form or detail the hub region of the wheel. However, in order to avoid significant undercuts that might lock a blow-molded wheel into its mold, the design of the tread surface on a blow-molded wheels is typically of limited complexity. In the case of blow-molded wheels used with children's ride-on vehicles, which are often intended to resemble full-sized vehicles, the limited complexity of the tread designs typically provided on blow-molded wheels limits the realism of the blow-molded wheels, which are often intended to resemble rubber tires.